This invention relates to a method of manufacturing an optical semiconductor device having a semiconductor optical waveguide.
Disclosure has been made about a conventional method of manufacturing a semiconductor optical waveguide on a semiconductor substrate by the use of the known selective metal-organic vapor phase epitaxy (MOVPE) method using a growth block mask in Proceedings (Journal of Crystal Growth Vol. 170, January 1997, pp. 634-638, K. Kudo et al.).
Conventionally, when an InP/InGaAsP based optical waveguide is formed by the use of the selective MOVPE growth, it is difficult to obtain sufficiently flat InGaAsP layer.
This main reason will be explained as follows.
Namely, a migration length of source material species is short on a surface of a semiconductor substrate. Consequently, the growth takes place before the source material species does not reach a center of a mask-opening portion.
As a result, a portion near the growth block mask of the opening portion (namely, a portion near a side surface of the formed optical waveguide) has a film thickness thicker than the center portion.
Further, a margin of growth condition for enlarging the migration of the source material species is conventionally reduced because the growth conditions suitable for the flatness are different from to each other with respect to the InGaAsP having a variety of compositions.